1. Technical Field
The present invention relates to an oscillator, an electronic apparatus, and a moving object.
2. Related Art
The reference frequencies used for backbone lines such as a synchronous optical network (SONET) and a synchronous digital hierarchy (SDH) are required to correspond to different frequencies from each other. For this purpose, equipment related to a transmission device used for backbone lines is provided with a plurality of oscillation units capable of respectively oscillating frequency signals different from each other, and is configured to select a certain oscillation unit to output a desired frequency signal, by a selection signal or the like from the outside.
For example, JP-A-2005-6130 discloses a two-frequency switching-type high-frequency quartz crystal oscillator including a first quartz crystal oscillation unit that outputs a first frequency signal, a second quartz crystal oscillation unit that outputs a second frequency signal, a first switch for supplying power to any one of the first quartz crystal oscillation unit and the second quartz crystal oscillation unit, by a selection signal from the outside, and a second switch that selects any one of the outputs of the first quartz crystal oscillation unit and the second quartz crystal oscillation unit, by a selection signal from the outside.
In this two-frequency switching-type high-frequency quartz crystal oscillator, the frequencies of the frequency signals which are output from the first quartz crystal oscillation unit and the second quartz crystal oscillation unit are adjusted, by controlling the capacitance of the variable-capacitance diode included in the first quartz crystal oscillation unit and the capacitance of the variable-capacitance diode included in the second quartz crystal oscillation unit by a frequency control voltage.
Further, the first quartz crystal oscillation unit further includes a resistor, and the characteristics of the above-described variable-capacitance diode and the resistor are appropriately selected, depending on the output frequency that is obtained by the first quartz crystal oscillation unit.
Similarly, the second quartz crystal oscillation unit also further includes a resistor, and the characteristics of the above-described variable-capacitance diode and the resistor are appropriately selected, depending on the output frequency that is obtained by the second quartz crystal oscillation unit.
The two-frequency switching-type high-frequency quartz crystal oscillator of such a configuration is easily miniaturized, as compared with the case of providing a structure for switching the application of the frequency control voltage, between the first quartz crystal oscillation unit and the second quartz crystal oscillation unit.
However, in the two-frequency switching-type high-frequency quartz crystal oscillator described in JP-A-2005-6130, since the line for applying a frequency control voltage is connected to both the first quartz crystal oscillation unit and the second quartz crystal oscillation unit at all times, when an alternating current (AC) component is superimposed on the frequency control voltage, the cutoff frequency (modulation bandwidth frequency) of the oscillator is influenced by the respective characteristics of the variable-capacitance diode and the resistor included in the first quartz crystal oscillation unit and the variable-capacitance diode and the resistor included in the second quartz crystal oscillation unit. For this reason, when the two-frequency switching-type high-frequency quartz crystal oscillator described in JP-A-2005-6130 is incorporated into a circuit, there is a possibility that the cutoff frequency of the AC component superimposed on the frequency control voltage changes significantly depending on the characteristics of the variable-capacitance diode and the resistor that are included in each quartz crystal oscillation unit, as compared to the related art. In other words, when using the two-frequency switching-type high-frequency quartz crystal oscillator described in JP-A-2005-6130, instead of the one-frequency type quartz crystal oscillator that is not a frequency switching type, there is a possibility that the cutoff frequencies of the AC component superimposed on the frequency control voltage before and after replacement are largely different from each other. In this way, if the cutoff frequencies are largely different, there is a possibility that the synchronization operation of the quartz crystal oscillation unit becomes unstable.